On 30 Aug 2009, at 11:36, Francisco Viramontes wrote:
Hi list!
I hava a question about grouping and the reduce function
If aI want to average the sum of manu values returned by my map
function on a large database (~100000 rows ) the reduce function
gets called with the rereduce boolean
The thing is a am not sure if its mathematically correct to average
sets of floats in groups as optimized by couch where I can have to
average smaller sets of previously averaged values. I certainly dont
get the exact same result of averaging a whole set than a grouped set.
My question is how can I handle my reduce function to reduce a whole
set and not in groups?
Note the emit call is done with complex keys:
map:
function(doc) {
if ((doc['couchrest-type'] == 'RawData') && doc
['device_variable_id']) {
date = new Date(doc.date_time);
emit([doc.device_variable_id, date.getFullYear(),
date.getUTCMonth() + 1, date.getUTCDate(), date.getUTCHours(),
parseInt(date.getUTCMinutes() / 20 + 1) ], doc.value);
}
}
reduce:
function( keys, values, rereduce ) {
if(rereduce){
log("rereduce");
}
return sum( values ) / values.length ;
}
You cannot ignore the call where rereduce is true. See
http://svn.apache.org/viewvc/couchdb/trunk/share/www/script/test/reduce.js?revision=804727&content-type=text%2Fplain
scroll down a little:
" var reduceCombine = function (keys, values, rereduce) { "
for an example.
